1. Field of the Invention
The present invention relates generally to an axial flow turbomachine designed so as to facilitate maintenance thereof, and more particularly to the construction of a maintenance-friendly axial compressor which may include variable guide vanes at an upstream end thereof.
2. Description of the Prior Art
Modern turbojet engines are generally of the twin spool type, that is to say they comprise two compressors, namely a low pressure compressor and a high pressure compressor, driven at different speeds by two turbines.
The last (i.e. downstream) stages of the high pressure (HP) compressor are subjected to high temperatures and to substantial wear. It is therefore desirable to provide easy access for inspection and maintenance of the fixed and movable blades of the last stages of the HP compressor.
However, in order to obtain better performance from the HP compressor, the clearances between rotor and stator are minimized by means such as variable guide vanes in the region of the first stages of the compressor, or by using a monobloc axisymmetrical casing. When these two means are used, maintenance of the downstream stages of the HP compressor becomes very difficult, since the monobloc axisymmetrical casing necessitates dismantling to be carried out from the upstream end, and the variable guide vanes situated at the upstream end must be taken down to gain access to the stages further downstream.
It is known, such as from French patent 2317480 and British patent 1488766, to design turbomachines with access openings passing through the casing or annular envelope surrounding a set of blades to permit maintenance of the blades. The drawback of such arrangements is that they provide access to only a restricted part of the turbomachine.
It is also known to construct compressor casings from half-shells, as well to form guide vane supports from annular members.